I like about 1"/3' of rod. I don't like the really long ones because it makes it harder to balance the rod. I would not go shorter than 4". My Albright has a really long one and added to it it's uplocking. If they were going to go that long they should have turned the seat around. My only complaint about the rod. You don't really need more than you can get your hand over. I tend to have part of my hand lower than the butt when I bomb one into the next time zone and then yell Piano!
I also go at least 1"/foot of rod for the top grip. I don't underhand cast though. I go 60-65% top hand. I don't end with the butt in my gut either. I don't have any real counter flex the way I do it and my rods are not fast. I have seen good scandi guys with rods that go doing the hula at the end of the cast. That has got to knock some serious distance off the cast.